The Narn are a mammalian species. The extreme conditions of the Narn homeworld have made the Narns a very sturdy race. Their thick skin allows them to live in comfort in both the sweltering heat and chilling cold (their skin is an efficient heat exchanger/retainer). Since their skin is so effective at temperature maintenance, Narns do not sweat -- keeping precious water sealed within their body. Their body also retains energy in a very efficient manner, allowing the Narns to hibernate for a maximum of six days without nourishment. Further, it allows them to eat only twice a day. Since their sun is a red giant, Narn eye sight is most sensitive in the orange to red spectrum. Though not as long lived as the Minbari, early middle age for Narns is approximately 50 to 60 standard years.
Though their outward appearance seems to be reptilian to Earthers, Narns are actually marsupials. The female bears the young, which are then cared for by the male Narn in his pouch. Narn physiology can allow physical intercourse with humans, but there can be no offspring unless there is extensive genetic engineering.